Data latch controller of synchronous memory device

ABSTRACT

Disclosed is a data input circuit of a synchronous memory device for detecting and amplifying data, and transferring the amplified data for storage, which including: a write strobe signal converter for receiving a write strobe signal, dividing the received write strobe signal, and outputting control signals of predetermined bits, the control signals being synchronized with rising and falling edges of the divided signal; and a latch unit for latching data corresponding to the bits by means of the control signals, and outputting the data for the detection and amplification of the data. The data input circuit may include a first delay unit for delaying the data in order to match setup-hold time, a second delay unit for performing delay for adjusting the data outputted from the latch unit, and a third delay unit for performing delay for adjusting the write strobe signal outputted from the latch unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a data input circuit of a synchronousmemory device, and more particularly to a data input circuit of asynchronous memory device, in which a data strobe signal can be used fora latch in a state of ensuring a full swing in a ultra high speedsynchronous memory device.

2. Description of the Prior Art

A Double Data Rate (DDR) 2 Synchronous Dynamic Random Access Memory(SDRAM), which is a high speed synchronous memory device, represents avolatile memory device for storing data in a cell including onetransistor and one capacitor. A DDR2 SDRAM synchronizes with an externalclock signal to perform an internal operation, and performs a datawrite/read operation in a 4-bit prefetch scheme.

Hereinafter, an operation in which the memory device synchronizes withan external clock signal to write data in a 4-bit prefetch scheme willbe described with reference to FIGS. 1 and 2.

A data input buffer 100 is a circuit for converting data inputtedthrough a data pin (DQ) to data of a CMOS level. A delay unit 110 is acircuit for delaying the data outputted from the data input buffer 100for a predetermined time period. An input data latch unit 120 is acircuit for latching the data outputted from the delay unit 110, andlatches 4-bit data in a 4-bit prefetch operation.

A WDQS buffer 150 is a circuit for converting a write strobe signal WDQSapplied from a memory controller to a signal of a CMOS level. The writestrobe signal WDQS represents a data strobe signal applied in a writeoperation. A delay unit 160 delays the write strobe signal WDQSoutputted from the WDQS buffer 150 for a predetermined time period, andoutputs both a rising strobe signal rdqs synchronized with the risingedge of the write strobe signal WDQS and a falling strobe signal fdqssynchronized with the falling edge of the write strobe signal WDQS.

The input data latch unit 120 synchronizes with the rising strobe signalrdqs and the falling strobe signal fdqs, and sequentially latches thedata.

The 4-bit data stored in the input data latch unit 120 are transferredto an input data detection amplifier 130 through internal lines align00, align 01, align 10 and align 11. The input data detection amplifier130 amplifies the 4-bit data respectively in response to a data inputstrobe signal Dinstrobe, and applies the amplified data to a writedriver 140. The write driver 140 stores the amplified data in a memorycell.

FIG. 2 is a waveform illustrating an operation of the data input unit ofthe memory device in FIG. 1.

Referring to FIG. 2, an “Ext clk” represents an external clock signalapplied to the memory device. A “WDQS” is the write strobe signal, whichrepresents a signal applied after predetermined time “tDQSS” from thetime point at which a write command is applied. The “tDQSS” correspondsto about 0.75 tCK˜1.25 tCK (tCK represents a period of the “Ext clk”)after the write command is applied. FIG. 2 shows 8-bit data continuouslyapplied through one data pin. Specifically, a “tDS” represents setuptime and a “tDH” represents hold time.

In the 4-bit prefetch operation, the 4-bit data, which have beenrespectively synchronized with the rising edges a and c and the fallingedges b and d of the write strobe signal WDQS, are aligned to thefalling edge d and applied to the input data detection amplifier 130.Likewise, next 4-bit data are synchronized and aligned in the samemanner and then applied to the input data detection amplifier 130. The4-bit data applied in parallel to the input data detection amplifier 130are synchronized with the data input strobe signal Dinstrobe and thenapplied to the write driver 140.

However, increase in the operation speed of the memory device causes thefollowing problems.

FIGS. 3 a and 3 b are diagrams illustrating transformation of a clocksignal in a high frequency operation.

As an operation frequency increases, the waveform of the write strobesignal WDQS transferred to the input data latch unit 120 via the delayunit 160 is transformed into an abnormal waveform as illustrated in FIG.3 b instead of a normal waveform as illustrated in FIG. 3 a. This isbecause a transmission line for connecting the delay unit 160 to theinput data latch unit 120 has a heavy load. Specifically, when the loadof the transmission line increases, an RC delay also increases.Therefore, the signal may be distorted.

If the write strobe signal WDQS having the abnormal waveform asillustrated in FIG. 3 b is applied to the input data latch unit 120, adesired operation cannot be performed. That is, the input data cannot beexactly latched and be aligned at an exact time point. As a result, theinput data cannot be normally written.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve theabove-mentioned problems occurring in the prior art, and an object ofthe present invention is to provide a signal generator available for ahigh speed memory device, thereby allowing a data latch operation to beperformed in the high speed memory device.

Another object of the present invention is to divide the frequency of anexternal input clock signal into ½ and use the divided clock signal asan internal control signal, thereby allowing a data latch operation tobe performed in the high speed memory device.

In order to achieve the above objects, according to one aspect of thepresent invention, there is provided a data input circuit of asynchronous memory device for detecting and amplifying data, andtransferring the amplified data for storage, the data input circuitincluding: a write strobe signal converter for receiving a write strobesignal, dividing the received write strobe signal, and outputtingcontrol signals of predetermined bits, the control signals beingsynchronized with rising and falling edges of the divided signal; and alatch unit for latching data corresponding to the bits by means of thecontrol signals, and outputting the data for the detection andamplification of the data.

It is preferred that the write strobe signal converter includes: a firstsignal generator for dividing the write strobe signal into ½ withreference to the rising and falling edges of the write strobe signal;and a second signal generator for generating the control signalsrespectively synchronized with the rising and falling edges of thedivided signal.

The first signal generator includes: a first flip-flop for outputtingthe signal synchronized with the rising edge of the write strobe signal;a first inverter for inverting the write strobe signal; and a secondflip-flop for receiving the inverted write strobe signal, and outputtingthe signal synchronized with the falling edge of the write strobesignal.

The second signal generator includes: a second inverter for invertingand outputting the signal synchronized with the rising edge of the writestrobe signal; a first switching element for delaying the signalsynchronized with the rising edge of the write strobe signal by delaytime of the second inverter, and outputting the delayed signal; a thirdinverter for inverting and outputting the signal synchronized with thefalling edge of the write strobe signal; and a second switching elementfor delaying the signal synchronized with the falling edge of the writestrobe signal by delay time of the third inverter, and outputting thedelayed signal.

The present invention further includes a first delay unit for delayingthe data in order to match setup-hold time, and providing the delayeddata to the latch unit.

The present invention further includes a second delay unit forperforming delay for adjusting the data outputted from the latch unit sothat the data correspond to an input time point of a data input strobesignal to be provided for the detection and amplification.

The present invention further includes a third delay unit for performingdelay for adjusting the write strobe signal outputted from the latchunit so that the write strobe signal correspond to an input time pointof a data input strobe signal to be provided for the detection andamplification, and providing the delayed signal to the write strobesignal converter.

It is preferred that the write strobe signal converter divides the datastrobe signal into ½.

It is preferred that the write strobe signal converter outputs thecontrol signal such that a high level interval of the control signal ismaintained for a time period for which a high level interval of thewrite strobe signal is maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of a data input circuit in a memory device forperforming a write operation in a 4-bit prefetch scheme;

FIG. 2 is a waveform illustrating an operation of a data input unit ofthe memory device in FIG. 1;

FIGS. 3 a and 3 b are diagrams illustrating transformation of a clocksignal in a high frequency operation;

FIG. 4 is a block diagram of a data input unit in a synchronous memorydevice according to one embodiment of the present invention;

FIG. 5 is a block diagram of the DQS converter in FIG. 4 according toone embodiment of the present invention; and

FIG. 6 illustrates waveforms of the control signals in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a preferred embodiment of the present invention will bedescribed with reference to the accompanying drawings.

FIG. 4 is a block diagram of a data input unit in a memory deviceaccording to one embodiment of the present invention.

A data input buffer 400 is a circuit for converting data inputtedthrough a data pin (DQ) to data of a CMOS level. FIG. 4 shows a case inwhich data are input through one data pin. Accordingly, a memory deviceincluding eight data pins may further include seven data input units,each of which is equal to the data input unit in FIG. 4. In this case,it is preferred to commonly use a WDQS buffer 460 and a DQS converter470 in all data input units.

A delay unit 410 is a circuit for delaying the data outputted from thedata input buffer 400 for a predetermined time period. The delay unit410 corresponds to a data delay adjustment circuit for matchingsetup-hold time of data.

An input data latch unit 420 is a circuit for latching the dataoutputted from the delay unit 410, and latches 4-bit data in a 4-bitprefetch operation.

A delay unit 430 is a circuit for receiving the 4-bit data having passedthrough the input data latch unit 420, delaying the received 4-bit datafor a predetermined time period, and outputting the delayed data. Thedelay unit 430 compensates for a difference of a tDQSS. It is commonthat a tDQSS is determined within the range of 0.75 tCK˜1.25 tCK.Accordingly, when the tDQSS is later than a reference value set by auser, the delay unit 430 decreases delay time. However, when the tDQSSis earlier than the reference value, the delay unit 430 increases thedelay time.

The WDQS buffer 460 is a circuit for converting write strobe signal WDQSapplied from a memory controller to a signal of a CMOS level.

The DQS converter 470 receives the data strobe signal WDQS of the CMOSlevel, which are outputted from the WDQS buffer 460, and generates fourtypes of control signals, i.e. rising strobe signals rdqs0 and rdqs1 andfalling strobe signals fdqs0 and fdqs1. The rising strobe signals rdqs0and rdqs1 and the falling strobe signals fdqs0 and fdqs1 correspond tosignals obtained by dividing the data strobe signal WDQS into ½,respectively. The rising edge of the rising strobe signal rdqs0synchronizes with the first rising edge of the data strobe signal WDQS,the rising edge of the falling strobe signal fdqs0 synchronizes with thefirst falling edge of the data strobe signal WDQS, the rising edge ofthe rising strobe signal rdqs1 synchronizes with the second rising edgeof the data strobe signal WDQS, and the rising edge of the fallingstrobe signal fdqs1 synchronizes with the second falling edge of thedata strobe signal WDQS. Each of the control signals rdqs0, rdqs1, fdqs0and fdqs1 has a high level interval maintained for a time period forwhich a high level interval of the data strobe signal WDQS ismaintained. FIG. 6 illustrates waveforms of the signals rdqs0 rdqs1,fdqs0, fdqs1, and WDQS.

The input data latch unit 420 sequentially latches the data whichsynchronize with the rising edges of the control signals rdqs0, fdqs0,rdqs1, and fdqs1 outputted from the DQS converter 470, and pass throughthe delay unit 410. In the 4-bit prefetch operation, the 4-bit datasynchronize with each of the control signals rdqs0, fdqs0, rdqs1, andfdqs1 and are latched by one bit. If the control signals rdqs0, fdqs0,rdqs1, and fdqs1 are inputted, the 4-bit data stored in the input datalatch unit 420 are aligned in parallel, and outputted to the delay unit430 through internal lines align 00, align 01, align 10 and align 11.

As described above, the delay unit 430 adjusts delay time of the input4-bit data in consideration of the time tDQSS. The data outputted fromthe delay unit 430 are synchronized with a data input strobe signalDinstrobe in the input data detection amplifier 440, are amplified, andthen stored in a corresponding memory cell by a write driver 450,respectively.

FIG. 5 is a block diagram of the DQS converter 470 in FIG. 4 accordingto one embodiment of the present invention. The DQS converter 470includes a first signal generator 500 and a second signal generator 510.The first signal generator 500 includes flip-flops 50 and 51 and aninverter 53, and the second signal generator 510 includes switchingelements 53 and 55 and inverters 54 and 56.

In FIG. 5, the flip-flop 50 receives an enable signal EN and the datastrobe signal WDQS, and the flip-flop 51 receives the enable signal ENand an inverted data strobe signal WDQS. Each of the output signals rdqsand fdqs of the flip-flops 50 and 51 has a frequency corresponding to ½of the data strobe signal WDQS. That is, each of the output signals rdqsand fdqs has a period which is two times as long as that of the datastrobe signal WDQS. The rising edge of the output signal rdqssynchronizes with the rising edge of the data strobe signal WDQS, therising edge of the output signal fdqs synchronizes with the falling edgeof the data strobe signal WDQS, and the high level intervals of theoutput signals rdqs and fdqs are maintained for a time period for whichthe high level interval of the data strobe signal WDQS is maintained.

FIG. 6 illustrates waveforms of the input and output signals of the DQSconverter 470 in FIG. 5. The switching element 53 receives the signalrdqs, and outputs the rising strobe signal rdqs0 according to the statusof operation voltages Vcc and Vss. The inverter 54 receives the signalrdqs and outputs the rising strobe signal rdqs1. The switching element55 receives the signal fdqs, and outputs the falling strobe signal fdqs0according to the status of the operation voltages Vcc and Vss. Theinverter 56 receives the signal fdqs and outputs the falling strobesignal fdqs1. Each of the switching elements 53 and 55 is a circuit formatching delay time of each of the inverters 54 and 56.

As described above, in order to latch data sequentially applied througha data pin, a signal WDQS is divided into ½, and 4-bit data are latchedby means of four types of control signals obtained by the division. Inthe prior art, as the operation frequency of a memory device increases,a signal is severely distorted due to RC delay in transmission ofcontrol signals. However, according to the present invention, a signalWDQS is divided, so that it is possible to use control signals for datalatch also in a high frequency operation. Since a 4-bit prefetchoperation is performed, 4-bit data aligned in parallel are applied tothe delay unit 430, and then transferred to the input data detectionamplifier 440. The delay unit 430 is provided in consideration of thefact that the time tDQSS of a data strobe signal WDQS is not constant.The delay time in the delay unit 430 can be optimally established inconsideration of relation with the data input strobe signal Dinstrobefor controlling the input data detection amplifier 440.

Specifically, since the delay unit 430 is provided for adjusting thetime tDQSS, the delay unit 430 may be disposed behind the WDQS buffer460 as in the prior art so long as the delay unit 430 normally operates.That is, the delay unit 430 may be disposed between the WDQS buffer 460and the DQS converter 470. Herein, in order to prevent a signal frombeing distorted, the WDQS buffer 460 must maintain a proper distancewith the DQS converter 470.

As described above, the present invention provides a scheme for dividinga data strobe signal WDQS for latching data applied in a write operationinto ½ and transferring the divided data, thereby preventing a memorydevice from abnormally operating due to signal distortion.

Further, the present invention can be usefully applied to a high speedsynchronous memory device having an operation frequency of more than 500MHz.

The preferred embodiment of the present invention has been described forillustrative purposes, and those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the invention as disclosed in theaccompanying claims.

1. The data input circuit of the synchronous memory device for detectingand amplifying data, and transferring the amplified data for storage,the data input circuit comprising: a write strobe signal converter forreceiving a write strobe signal, dividing the received write strobesignal, and outputting control signals of predetermined bits, thecontrol signals being synchronized with rising and falling edges of thedivided signal; and a latch unit for latching data corresponding to thebits by means of the control signals, and outputting the data for thedetection and amplification of the data; wherein the write strobe signalconverter comprises: a first signal generator for dividing the writestrobe signal into ½ with reference to the rising and falling edges ofthe write strobe signal; and a second signal generator for generatingthe control signals respectively synchronized with the rising andfalling edges of the divided signal.
 2. The data input circuit asclaimed in claim 1, wherein the first signal generator comprises: afirst flip-flop for outputting the signal synchronized with the risingedge of the write strobe signal; a first inverter for inverting thewrite strobe signal; and a second flip-flop for receiving the invertedwrite strobe signal, and outputting the signal synchronized with thefalling edge of the write strobe signal.
 3. The data input circuit asclaimed in claim 1, wherein the second signal generator comprises: asecond inverter for inverting and outputting the signal synchronizedwith the rising edge of the write strobe signal; a first switchingelement for delaying the signal synchronized with the rising edge of thewrite strobe signal by delay time of the second inverter, and outputtingthe delayed signal; a third inverter for inverting and outputting thesignal synchronized with the falling edge of the write strobe signal;and a second switching element for delaying the signal synchronized withthe falling edge of the write strobe signal by delay time of the thirdinverter, and outputting the delayed signal.